The present invention is generally related to locomotives and, in particular, to an auxiliary power system of a locomotive.
A diesel-electric locomotive typically includes a diesel engine coupled to drive a main alternator and a set of auxiliary alternators, made up of several physically distinct alternators. The main alternator is coupled to power one or more traction motors, and the auxiliary alternator set is coupled to power locomotive auxiliary electrical equipment. The auxiliary alternator set may include a first alternator for powering a battery, a second alternator for powering auxiliary equipment, and a third alternator for providing field excitation to the auxiliary alternator and the traction alternator.
It is known to provide variable frequency and/or voltage by way of inverters so that the auxiliary equipment may be driven at any speed below or above the engine speed. The auxiliary equipment is generally operable in an electrical power consumption mode but may be capable of at least transiently entering into an electrical power-generating mode. For example, due to windy conditions and prior to turn on, a cooling fan may be rotating opposite to its normal direction of rotation and during such a condition the cooling fan would generate electrical power. It is known that this power generating condition has necessitated either the addition of power dissipating resistor elements or, in lieu of using straightforward diode rectifiers, designers may be forced to use relatively costlier regenerative rectifier drives. Either of these options is not fully satisfactory since each entails incremental costs and undue complexity for the auxiliary power system of the locomotive. Thus, it would be desirable to provide system and techniques that allow to divert electrical power that may be generated by the auxiliary equipment in a manner that avoids or reduces such incremental costs and complexity and allows for useful utilization of such electrical power, as opposed to merely dissipating such electrical power into heat.
As noted above, the auxiliary alternator in known auxiliary power systems for locomotives is traditionally made up of three physically distinct alternators. This consumes valuable and scarce space in the locomotive and requires careful analysis of mechanical resonances that may develop along the common shaft that mechanically interconnects these distinct alternators to the internal combustion engine of the locomotive. Thus, it would be desirable to provide a locomotive auxiliary power system wherein the auxiliary alternator comprises just a single alternator that may be connected through a single shaft to the internal combustion engine.
U.S. Pat. No. 6,486,568, assigned in common to the same assignee of the present invention discloses innovative techniques regarding a power system for a locomotive, including an option that allows removing altogether the auxiliary alternator for powering the auxiliary bus of the locomotive. It is noted that traditional auxiliary equipment (such as may part of a fleet of field-deployed locomotives) is generally operated at a different voltage than the operating voltage of the traction motors. For example, the traction motors may be typically operated at a relatively higher voltage, while the auxiliary equipment may be operated at a relatively lower voltage. Accordingly, if the voltage level of a common bus, or bus voltage, for powering both the traction motors and the auxiliary equipment is set to a voltage level appropriate for powering the traction motors, the auxiliary equipment may not be able to be directly connected to the bus because the bus voltage is different from the voltage required to power the auxiliary equipment. Thus, it would be desirable to provide a locomotive power system with a common bus for powering the traction motors and the auxiliary equipment and configured to enable such auxiliary equipment to be compatible with the voltage level available at that common bus.